In which I will be keeping track (for my own benefit) of my daily progress in the identification of the ant fauna of Tiputini Biodiversity Station in Ecuador, the analysis of that data, and the pursuit of my PhD. And (for the benefit of everyone else) I hope to provide helpful information on ants, taxonomy, database management, identification, and other assorted endeavors. Cheers

Tuesday, November 14, 2006

This is one of my favorite things about ants -- the ant death spiral. Actually, it's a circular mill, first described in army ants by Schneirla (1944). A circle of army ants, each one following the ant in front, becomes locked into a circular mill. They will continue to circle each other until they all die. How crazy is that? Sometimes they escape, though. Beebe (1921) described a circular mill he witnessed in Guyana. It measured 1200 feet in circumference and had a 2.5 hour circuit time per ant. The mill persisted for two days, "with ever increasing numbers of dead bodies littering the route as exhaustion took its toll, but eventually a few workers straggled from the trail thus breaking the cycle, and the raid marched off into the forest."

Folks interested in things like self-organization, emergant properties, complex systems, etc. etc. like to point to this as a cautionary tale. I even found a reference to a group programming robots to interact like ants that accidentally produced this behavior in their robots. Apparently you can also reproduce this behavior in the lab by placing a glass jar into the surface. The ants will eventually circle the jar and continue to do so even after the jar has been removed. I assume just army ants. Wow, I wish we had an army ant colony in the lab.

Anyway, in tribute to this fabulously bizarre phenomenon, I made some Ant Death Spiral T-shirts. Check them out!Other references:

Ants are around for over 100 million years. So in my opinion this behavior either must be very infrequent or probably has some positive effect, otherwise evolution would have rooted that behavior out. Perhaps the conditions to make a death spiral occur are kinda unnatural, e.g. man-made roads as shown in the video from Panthanal.

This is an incorrect assumption often confused outside of the scientific theory of evolution and how it works. While it is likely infrequent, it does not have to have a positive effect, it simply needs to carry on for multiple generations. For example arthritis is rather detrimental, but it's existence does not mean it is a positive attribute, it is a trade off for the ability to flex joints. Many cases exist where a condition has been adopted through evolution and either harms or has no effect on the organism. What this really is a great example of is an infinite loop, such as in programming. The ant is likely supposed to follow the one in front, and nearly always works efficiently, until the "front" ant (which is really any of them) begins to follow the back, and thus the infinite loop is created. While it is possible for human interaction to cause this, it is much more likely an anomaly that happens because of an inherited trait (not because ants are completely boggled by roads, but because they follow the ant in front of them).

Demesos: If you were correct, we wouldn't suffer from allergies or auto-immune disease. It would probably help to remember that we're not at the end of the evolutionary cycle. If you went to only 50 million years into the evolution of ants, would you say "well, that's a really long time, surely all their bad traits have been bred out?" Probably not, and there's no reason to think 100 million is enough either.

Also, if a trait is detrimental but generally doesn't completely prevent reproduction (such as male pattern baldness) the trait can stick with the species.

BUT, more to the point about the article, I think the closest analog in the business world is rule by committee. Rather than making decisions, middle managers tend to pass the ball around, hold meetings, create reports, discuss holding more meetings, "touch base," identify positive action steps, blah blah blah. No one is willing to make a decision and issue orders.

I'm sure that you're probably aware of the NetLogo simulation program (massively parallel, intelligent agents)at Northwestern (http://ccl.northwestern.edu/netlogo/) They have a pre-designed model of ant behavior searching for, finding food, and carrying it back to the nest. If the model is correct, such behavior could be created by a flaw in pheromone production, like continuously signaling food when none is available.

@ Anonymous: I don't disagree. As I said: _either_ being infrequent (which means infrequent enough to not impair reproduction of the organism) or, if not the first then coming with some other effect that compensates for this weakness.@ BL1Y: "allergy" is definitive a negative trait, but it comes with a powerful immune system which has a positive effect. So, existence of allergies fits my example, not contradict it.